It is probably that a large percentage of Mexican population is in an asymptomatic phase after been infected with Trypanosoma cruzi (T. cruzi), protozoan that causes Chagas disease, according with Guiehdani Villalobos Castillejos, PhD in Chemical and Biological Sciences by the National School of Biological Sciences at the National Polytechnic Institute (IPN), who has studied the vector of this disease for years.
She explained that although Chagas disease can be contracted from an early age, the chronic disease manifests until the productive stage of the person, i.e. 30 or 40 years old, decreasing labor productivity of the infected due to health problems.
In an interview, Villalobos Castillejos gave an overview of this condition. She explained that it is called Chagas after the scientist who discovered it in 1909, the Brazilian Carlos Chagas. She explained that this is a unique case in medicine research, since the same researcher identified the parasite that causes it (T. cruzi), the vector (triatomine bug, also known as kissing bug) and its human pathology.
“Originally, the physician (Carlos Chagas) was studying malaria in a Brazilian community. He saw some rare parasites in human blood and also noted that there were many bugs. He began to analyze (the bugs) and found the same parasite in them,” she said.
Chagas disease is also known as American trypanosomiasis, because T. cruzi only exists in America, unlike his “brother”, Trypanosoma brucei (T brucei) that is found in Africa, Guiehdani Villalobos said.
T. cruzi is found in wild mammals, domestic reservoirs (dogs, cats and other animals that we have at home) and in humans, said the researcher.
“A bug infected with T cruzi parasite comes out of his lair, feeds on the blood of a host, and while it feeds, defecates. The parasites are found in the feces. Unlike other insects such as mosquitoes that transmit parasites through saliva, triatomine cause infection by the mechanical reaction to the bite: it itches, you scratch lacerating the skin, and the parasite enters the bloodstream,” she said.
She explained that there is a stage called acute phase in humans. In this phase, the parasite is found in the bloodstream and is easily detected with parasitological tests, i.e. a blood test.
After a few weeks, the parasite invades tissues. In Mexico the parasite invades the heart, and in South America it goes more often to the intestine or colon, he said Villalobos Castillejos.
According to the specialist, a person may remain without symptoms over a number of years. When the host is around 30, the disease develops into a symptomatic chronic phase, in which the heart or the gut grow in size, resulting in the death of the host.
Besides kissing bug bites, there are other forms of transmission of Chagas disease: blood transfusion, organ transplantation, infection from mother to child, laboratory accidents and, in some cases, oral transmission, said Dr. Villalobos Castillejos.
“There is a case in a community in South America, where juices were prepared without proper hygiene. They did not realize that the fruits had bugs. They mashed it, drank the juice and many people were contaminated orally,” she explained.
She also explained that in Spain, where Chagas disease is not endemic, it has been reported contagion cases of this disease through blood transfusions of people who came or traveled to America and have the disease.
“But the main route of infection is by the vector. Is not sexually transmitted or by using contaminated syringes, as in the case of AIDS,” she said.
Laboratory work to address the problem
Currently, Dr. Guiehdani Villalobos Castillejos is studying if T cruzi affects the life cycle of the kissing bug. “We wonder if an infected bug arrives faster to adulthood than one that is not. Because if so, it reproduces earlier, having more offspring. For Chagas disease, having more vectors will increase the number of times that the bug will bite a human,” she said.
“We are also observing the biological characteristics of the bug to see if the protozoan is really affecting it and how: in a good, bad or in complicity way. Because maybe the bug is infected and dies, but gets faster to adulthood, which for biological purposes is to reach the reproductive stage,” she said.
Another line of research, the specialist is working on, involves directly studding T cruzi. They have identified six groups of the parasite.
In Mexico most people who describe the parasite identifies it with a single lineage. However, in South America and recent reports in Mexico indicate that there is not only one genetic group, but there are many. However, they are poorly studied, she said.
The research team is studying if there is only one T cruzi group adapted to the kissing bug, or if it is the only one that exists. “What we are doing now is infecting the bug with different genetic groups and see which one fits better in the gut of the vector, to see if there really is co-evolution of the parasite with kissing bug in Mexico,” she explained.
By knowing the biology of the insect (like how the parasite behaves in its gut), it is possible to identify potential targets and then develop vaccines and other strategies to avoid transmissions, concluded the expert.
Source: Agencia Informativa CONACYT